This invention relates to a sealed motor-compressor unit for refrigeration systems, or more particularly, to a refrigerating machine oil to be supplied for the compressor composing the sealed motor-compressor unit mentioned above.
Conventionally, as far as a refrigerating machine oil to be supplied for the compressor composing the sealed motor-compressor unit constituting a refrigerating cycle is concerned, refrigerating machine oil of ISO-VG 32 grade (more specifically, International Organization for Standardization VG 32 grade), the kinetic viscosity of which is defined to be 27 to 35 centistokes, has been employed for use in common.
However, in the case of the sealed motor-compressor provided with the power rating less than one horse power, the power rating of the motor included in the sealed motor-compressor is not sufficient to fully cope with variations in loads to be often effected in connection, for example, with the unsteady operation. Therefore, under these circumstances as described above, as long as such the refrigerating machine oil of ISO-VG 32 grade having a relatively high kinetic viscosity and thus, providing a rather high oil film or shearing resistance at an ordinary lubricating process, is to be employed, the faulty actuation concerning the sealed motor-compressor will not be avoidable. As a matter of fact, the disadvantages as described above may be especially frequently encountered under a rather low temperature condition, subject to the fact that the initial working load caused by the oil film shearing resistance will be increased in association with the decrease of the environmental temperature. Furthermore, if the machine oil mentioned above has a much higher viscosity due to the reasons as described above, the amount of machine oil to be fed tends to be decreased and thus, the occurrence of undesirable friction loss to be involved in respective sliding portions of the compressor composing the sealed motor-compressor unit has not been avoided.
Accordingly, a refrigerating machine oil especially suitable for use in a sealed motor-compressor unit, particularly constituting a refrigerating cycle and is provided with a motor not having a sufficient reverse capacity in the electric rating against variations in loads, has been strongly demanded.